Composite concrete pavement for highways and streets with the enriched quarry limestone waste as a coarse aggregate for concrete of subbase and/or lower layer

ABSTRACT

Composite concrete pavement includes the surface course of normal concrete and subbase and/or lower layer of concrete with coarse aggregate defined as enriched limestone waste of grading intermediate between the coarse and fine aggregates. Specified compressive strength and modulus of rupture of this concrete amount up to 5,000 and 750 psi, respectively.  
     Coarse aggregate of this concrete is enriched by-product of manufacture of crushed limestone of regular sizes. As a raw material for enrichment it should be coarser than 9.5 mm and finer than 4.75 mm. The amount of aggregate finer than 4.75 mm as a part of the total weight of aggregate should be not less than ⅓ before enrichment and close to but not exceed ⅔ in aggregate bin.  
     The use of this very cheap and efficient concrete for composite concrete pavement allows reduction of initial cost of construction of this pavement and makes it more competitive as compared with asphalt pavement.

REFERENCE TO RELATED APPLICATION

[0001] Provisional Patent Application No. 60/446408 Filing Data Feb. 11,2003

FEDERALLY SPONSORED RESEARCH

[0002] Not Applicable

SEQUENCE LISTING PROGRAM

[0003] Not Applicable

BACKGROUND

[0004] 1. Field of Invention

[0005] Present invention relates to the design and construction ofhighway and street concrete pavements.

[0006] 2. The Prior Art

[0007] Composite concrete pavements with surface course of normalconcrete and subbase or lower layer of lean concrete are used widely inthe US building practice to reduce the cost of pavement. The designprocedure of Portland Cement Association Engineering Bulletin (ThicknessDesign for Concrete Highway and Street Pavements, Portland CementAssociation, EB 109P) indicates a thickness for two-layer concretepavement equivalent to a given thickness of normal concrete. Leanconcrete of modulus of rupture (MR) in the range from 150 to 450 psi forsubbase and lower layer monolithic with normal concrete of surfacecourse is taken for design charts of composite pavement.

[0008] Design procedure of the normal concrete pavement results in thecertain value of normal concrete thickness. The sense of compositepavements of the identical capacity is in the reduction of consumptionof normal concrete with high cost crushed granite as a coarse aggregateby replacing of a part of this concrete by subbase or lover layercheaper concrete. Design procedure of composite concrete pavement shouldresult in the equivalent normal concrete thickness of the same value asfor the corresponding normal concrete pavement. The choice of flexuralstrength for subbase and lover layer of composite concrete pavement isdetermined by the merely economical reasons. Increase of flexuralstrength of concrete of subbase or lower layer means the increase ofequivalent thickness of normal concrete pavement and possibility ofcorresponding reduction of thickness of normal concrete surface courseof this pavement. Increase of equivalent normal concrete thickness ofcomposite pavement due to increase of flexural strength of concrete ofsubbase without changing of the thickness of subbase can be consideredapproximately as a measure of possible reduction of thickness of surfacecourse of this pavement.

[0009] Design chart for composite concrete pavement with lean concretesubbase of modulus of rupture in the range from 150 to 450 psi ispresented on the FIG. B1, Appendix 2 of said Portland Cement AssociationEngineering Bulletin. It allows estimation of equivalent normal concretethickness of composite concrete pavement corresponding to the differentcombinations of thickness of lean concrete subbase and normal concretesurface course of pavement.

[0010] The values of equivalent normal concrete thickness of pavementcorresponding to the lean concrete 4-inch thickness subbase of modulusof rupture in the range from 150 to 450 psi and values of thickness ofsurface course in the range from 7 to 10 inches were estimated accordingto this design chart. It allows estimation of the change of equivalentthickness of composite pavement depending on the change of lean concreteflexural strength of subbase. Moreover, relative increase of thisthickness depending on the increase of modulus of rupture of leanconcrete of subbase were carried out, equivalent normal concretethickness corresponding to the value of modulus of rupture equal to 150psi being considered as 1,0. Results of these calculations are presentedin Table 1. TABLE 1 Modulus of rupture of normal concrete of Modulus ofrupture of normal concrete of surface course in the range 600 to 700 psisurface course in the range 500 to 600 psi Modulus of rupture of 4-inchthickness Modulus of rupture of 4-inch thickness lean lean concretesubbase, psi concrete subbase, psi Thickness 150 250 350 450 150 250 350450 of normal Equivalent normal concrete thickness of composite pavement(inch) and relative concrete increase of this thickness depending on theincrease of modulus of rupture of lean surface concrete of subbase(equivalent normal concrete thickness corresponding to the value course(inch) of modulus of rupture equal to 150 psi is considered as 1.0) 7 8.5/1.0  9.1/1.07  9.5/1.12  9.9/1.2  8.6/1.0  9.2/1.07 10.0/1.1610.4/1.2  8  9.6/1.0 10.2/1.07 10.7/1.11 11.2/1.16  9.8/1.0 10.5/1.0711.0/1.12 11.5/1.17 9 10.6/1.0 11.3/1.07 11.8/1.11 12.3/1.16 10.9/1.011.5/1.06 12.2/1.12 12.6/1.16 10  11.6/1.0 12.4/1.07 12.9/1.11 13.4/1.1611.9/1.0 12.6/1.06 13.4/1.12 13.8/1.16

[0011] As can be seen from the Table 1, increase of equivalent normalconcrete thickness of composite pavement due to increase of modulus ofrupture of concrete of subbase from 150 to 450 psi constitutes at least15%. It can be considered as estimation of corresponding reduction ofthe thickness of normal concrete surface course.

[0012] Moreover, efficiency of composite pavement with lean concretesubbase can be estimated as a ratio of equivalent normal concretethickness of composite pavement to physical one (thickness of subbaseplus thickness of surface course). Estimations of this ratiocorresponding to the values of modulus of rupture of concrete in therange from 150 to 450 psi, the values of thickness of subbase equal 4,5, and 6 inches, and the values of normal concrete surface course in therange from 7 to 11 inches were calculated according to design chart FIG.B1 of said Engineering Bulletin. Average cstimations of this ratio arepresented in the Table 2. TABLE 2 Modulus of rupture of Modulus ofrupture of normal concrete of surface normal concrete of surface coursein the range course in the range 600 to 700 psi 500 to 600 psi Modulusof rupture of lean Modulus of rupture of lean concrete of subbase, psiconcrete of subbase, psi Thickness 150 250 350 450 150 250 350 450 oflean Ratio between equivalent normal concrete concrete thickness ofcomposite concrete pavement subbase in. and physical one of thispavement 4 0.803 0.856 0.902 0.936 0.829 0.877 0.923 0.962 5 0.786 0.8350.897 0.912 0.810 0.858 0.906 0.950 6 0.707 0.819 0.864 0.864 0.7930.840 0.895 0.944

[0013] It is evident that the efficiency of the use of lean concrete forcomposite concrete pavements increases with the reduction of thedifference between the values of modulus of rupture of normal concreteof surface course and the lean concrete of subbase. The compressive andflexural strengths of lean concrete are determined to a great extent bythe quality of coarse aggregate. Lean concrete can be produced whenlocal or recycled, relatively cheap coarse aggregates are available; thecost of concrete is determined to a large degree by the cost of coarseaggregate. The use of cheap small grains coarse aggregates is the one ofthe way of obtaining of lean and not only lean concrete. The name ofRussian standard GOST 26633 is “Normal and small grains concrete”.

[0014] Small grains crushed limestone is one of the cheapest aggregates.According to the US Geological Survey, crushed limestone constitutes 71%of total weight of coarse aggregates for concrete produced in USA. Thisproduct of grading finer than 9.5 mm usually is not used as a coarseaggregate. Utilization of great deposits of crushed limestone finer than9.5 mm and especially finer than 4.75 mm (from 10 to 25% of the totalvolume of quarrying) are urgent for aggregate industry. The object ofdesign of composite concrete pavements is to obtain the highest concretestrength of subbase and lower layer of this pavement with the cheapestcoarse aggregate and with the moderate consumption of cement.

OBJECTS AND ADVANTAGES

[0015] The main object of the present invention is to obtain compositeconcrete pavement for highways and streets with the thickness of normalconcrete surface course determined by requirements for the abrasionresistance and lower layer of concrete with the coarse aggregate definedas enriched limestone waste, lower layer being monolithic with thesurface course. Compressive and flexural strength of concrete of lowerlayer can be at least close to that for concrete of surface course.Concrete of lower layer requires consumption of cement, which is less orat least close to that for concrete of surface course of the samecompressive strength with crushed granite as a coarse aggregate.

[0016] Another important object of the present invention is to obtaincomposite concrete pavement for highways and streets with the surfacecourse of thickness determined by requirements for the abrasionresistance and subbase of concrete with the coarse aggregate defined asenriched limestone waste. Compressive and flexural strength of concreteof subbase can be at least close to that for concrete of surface course.Concrete of subbase requires consumption of cement, which is less or atleast close to that for concrete of surface course of the samecompressive strength with crushed granite as a coarse aggregate.

[0017] Still another important object of the present invention is toobtain composite concrete pavement for highways and streets with thethickness of normal concrete surface course determined by determined byrequirements for the abrasion resistance, lower layer and subbase ofconcrete with the coarse aggregate defined as enriched limestone waste.Compressive and flexural strength of concrete of lower layer and subbasecan be at least close to that for concrete of surface course. Concreteof lower layer and subbase requires consumption of cement, which is lessor at least close to that for concrete of surface course of the samecompressive strength with crushed granite as a coarse aggregate.

[0018] The most important object of present invention is to obtainconcrete with the coarse aggregate as a processed by-product of regularsizes crushed limestone manufacture defined as enriched limestone waste.Grading of this aggregate is intermediate between coarse and fineaggregates in Terminology of ASTM C125. Compressive and flexuralstrength of concrete with this coarse aggregate should be higher or atleast close to that for concrete of the same consumption of cement withcrushed granite of regular sizes number as a coarse aggregate.

[0019] The main advantage of present invention is the feasibility ofobtaining of concrete with the values of specified compressive strengthand modulus of rupture up to 5,000 psi and more than 750 psi,respectively, using processed by-product of manufacture of crushedlimestone of ordinary sizes defined as enriched limestone waste as acoarse aggregate. It does not require excessive consumption of cement;amount of consumed cement for this concrete is less or at least close tothat for concrete of the same compressive and flexural strength withcrushed granite and crushed limestone of the ordinary sizes as a coarseaggregate.

[0020] Another important advantage of present invention is thepossibility of construction of composite concrete pavement using verycheap concrete of compressive strength and modulus of rupture up to5,000 psi and more than 750 psi, respectively, with the enrichedlimestone waste as a coarse aggregate for of subbase and/or lower layerof this pavement. Consumption of cement for concrete with the enrichedlimestone waste as a coarse aggregate is less or at least close to thatfor concrete of surface course of the same compressive strength withcrushed granite of regular sizes as a coarse aggregate. Compressive andflexural strength of concrete for subbase and/or for lower layer can benot less than that for surface course of this pavement. As a result,equivalent normal concrete thickness of composite concrete pavement canbe close to physical one of this pavement.

[0021] Yet another important advantage of present invention is thepossibility to use limestone quarry waste as a coarse aggregate ofconcrete instead of high-quality aggregate. It allows very profitableutilization of great deposits of crushed limestone finer than 9.5 mmusually estimated as limestone quarry waste and especially aggregatefiner than 4.75 mm. In so doing the volume of utilized aggregate finerthan 4.75 mm should constitutes at least ⅓ of the volume of utilizedaggregate finer than 9.5 mm. Utilization of limestone waste enables toreduce quarrying of high-quality aggregate with correspondingconservation of environment.

SUMMARY OF INVENTION

[0022] Composite concrete pavement includes normal concrete surfacecourse of thickness determined by requirements for the abrasionresistance of surface and subbase or subbase and lower layer. Concreteof subbase and lower layer with coarse aggregate defined as enrichedlimestone waste of grading intermediate between coarse and fineaggregates in Terminology of ASTM C125 is characterized by specifiedcompressive strength f_(c)′ and modulus of rupture (MR) up to 5,000 andmore than 750 psi, respectively. This aggregate is processed by-productof manufacture of crushed limestone of ordinary Sizes number 56, 57, 6,and 67 with the rated dimensions 25-9.5 mm, 25-4.75 mm, 19-9.5 mm, and19-4.75 mm, respectively. The aim of enrichment of limestone quarrywaste is the reduction of small sizes of grains. Enrichment of thisaggregate should be carried out by washing or screening, or bycombination of washing and screening. Method of enrichment depends onthe grading of aggregate and should be selected by economical reasons.

[0023] Limestone quarry waste as a raw material for enrichment should befiner than 9.5 mm but coarser than 4.75 mm. The amount of aggregatefiner than 4.75 mm (Sieve No.4) before enrichment should be at least thevalue of the same order as for the least Size of coarse aggregate number89 according to ASTM C33, and it should be not less than ⅓ of the totalweight of aggregate. After enrichment the main part of aggregate finerthan 4.75 mm should be coarser than 2.36 mm. The amount of aggregatefiner than 2.36 mm (Sieve No. 8) should not exceed about 10%; the amountof aggregate finer than 1.18 mm (Sieve No. 16) should not exceed about7%; the amount of aggregate finer than 300 μm (Sieve No. 50) should notexceed about 2%.

[0024] Handling and transportation of enriched limestone waste from aquarry to the aggregate bin of a concrete plant causes inevitablebreakdown of aggregate. Due to weather effects and other impacts such asloading and discharge, grading of enriched limestone waste may becomeunpredictable. However, few parameters of grading of enriched limestonewaste after transportation from a quarry to the aggregate bin of aconcrete plant should be controlled in the framework of the presentinvention. The amount of aggregate finer than 4.75 mm (Sieve No.4)should be less than that for largest Size of fine aggregate number 9according to ASTM C 33. It should be close to but not exceed ⅔ of thetotal weight of aggregate. The amount of aggregate finer than 300 μm(Sieve No. 50) should not exceed about 3.0%. Grading of enrichedlimestone waste after transportation from a quarry to the aggregate binof a concrete plant can be considered as intermediate between coarse andfine aggregates in the Terminology of ASTM C125.

[0025] The compressive and flexural strength of the concrete of thesubbase and the lower layer with enriched limestone waste as a coarseaggregate can be not less than that for normal concrete of the surfacecourse of this pavement. The amount of consumed cement for subbase andlower layer is less or at least close to that for normal concrete of thesame compressive strength with crushed granite of regular sizes as acoarse aggregate. As a result of the use of concrete with the differentcost but with the same compressive and flexural strength for differentparts of composite pavement, the equivalent normal concrete thickness ofthis pavement is close to the physical one.

[0026] Concrete of specified compressive strength and modulus of ruptureup to 5,000 more than 750 psi, respectively, with enriched limestonewaste as coarse aggregate is very cheap and efficient. The use of thisconcrete for composite concrete pavement means considerable reduction ofinitial cost of construction this pavement and increase ofcompetitiveness as compared with asphalt pavement.

[0027] Moreover, the use of concrete with this coarse aggregate allowsvery profitable utilization of great deposits of crushed limestone finerthan 9.5 mm usually estimated as limestone quarry waste and especiallyaggregate finer than 4.75 mm. In so doing the volume of utilizedaggregate finer than 4.75 mm should constitutes at least ⅓ of theutilized volume of aggregate finer than 9.5 mm. Utilization of limestonewaste enables to reduce quarrying of high-quality aggregate withcorresponding conservation of environment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0028] Composite concrete pavement includes normal concrete surfacecourse with the thickness determined by the requirements for abrasionresistance of surface and subbase and/or lower layer monolithic with thesurface course. Processed by-product of manufacture of crushed limestoneof regular sizes defined conventionally as enriched limestone waste ofgrading intermediate between the coarse and fine aggregates in theTerminology ASTM C125 is used as a coarse aggregate for concrete ofsubbase and/or lower layer of this pavement. This concrete ischaracterized by the specified compressive strength f_(c)′ and modulusof rupture (MR) up to 5,000 and more than 750 psi, respectively.Consumption of cement for concrete with enriched limestone waste of thisgrading as a coarse aggregate is less or at least close to that forconcrete of the same compressive and flexural strength with crushedgranite of regular sizes as a coarse aggregate.

[0029] Portland Cement Association Engineering Bulletin (ThicknessDesign for Concrete Highway and Street Pavements, Portland CementAssociation, EB 109P) provides thickness design of composite concretepavement with lean concrete of subbase and lower layer of modulus ofrupture in the range of 150-450 psi. The use of enriched limestone wasteof grading intermediate between the coarse and fine aggregates in theTerminology ASTM C125 as a coarse aggregate of concrete for subbase andlower layer of composite concrete pavement allows to increase flexuralstrength of these parts of pavement. In spite of the differences ofcomposition and cost of concrete for surface course and subbase and/orlower layer their compressive and flexural strengths can be similar. Inthis case equivalent normal concrete thickness of this compositepavement determined according to said Engineering Bulletin is close tophysical one.

[0030] Enriched limestone waste is cheap coarse aggregate, and itconsiderably determines the cost of concrete. The use the concrete withthis coarse aggregate allows to reduce initial cost of construction andshould make concrete pavements more competitive as compared with theasphalt pavements.

OPERATION OF PREFERRED EMBODIMENT

[0031] Portland Cement Association Engineering Bulletin (ThicknessDesign for Concrete Highway and Street Pavements, Portland CementAssociation, EB 109P) contents design charts for composite concretepavement with subbase and lower layer of lean concrete with the valuesof modulus of rupture in the range of 150-450 psi. This design procedureindicates a thickness for two-layer concrete pavement equivalent to agiven thickness of normal concrete. The efficiency of composite pavementcan be estimated as a ratio of equivalent normal concrete thickness ofpavement to the physical one of this pavement.

[0032] Said Portland Cement Association Engineering Bulletin does notprovide thickness design of composite concrete pavement with modulus ofrupture of subbase or lover layer higher than 450 psi. However modulusof rupture of concrete with enriched limestone quarry waste as a coarseaggregate for subbase and lower layer of composite pavement can exceed450 psi. Moreover, it can be not less than that for the normal concreteof surface course of this pavement. In this case equivalent normalconcrete thickness of composite pavement is equal to the physical one ofthis pavement, and the ratio of equivalent normal concrete thickness ofpavement to the physical one is estimated as unity.

[0033] Equivalent normal concrete thickness of composite pavement withmodulus of rupture of concrete for subbase and lower layer intermediatebetween 450 psi and that for surface course should be estimated by, theratio of equivalent normal concrete thickness of this pavement to theits physical one. This ratio is in the range from that corresponding tothe composite concrete pavement of value of modulus of rupture ofconcrete of subbase or lower layer equal to 450 psi (Design charts FIG.B1 and B2 of said Engineering Bulletin) to the unity. The ratio ofequivalent normal concrete thickness to the its physical one forpavement of modulus of rupture of subbase and lover layer, which ishigher than 450 psi but less than modulus of rupture of surface course,should be estimated by interpolation.

[0034] For example, equivalent normal concrete thickness of compositepavement of the 5-inches thickness subbase of concrete of modulus ofrupture equal to 450 psi and 10-inches thickness normal concrete surfacecourse of modulus of rupture equal to 700 psi can be estimated as 14inches. The ratio of the equivalent normal concrete thickness to thephysical one of this pavement (15 inches) is equal to 0.933. It isnecessary to determine the equivalent normal concrete thickness ofcomposite concrete pavement of the same dimensions and the same flexuralstrength of surface course but with the concrete of subbase of modulusof rupture equal to 600 psi. It should be estimated by the ratio ofequivalent normal concrete thickness of this pavement to its physicalone. This ratio should be estimated by interpolation between thatcorresponding to the composite concrete pavements of the values ofmodulus of rupture of concrete of subbase or lower layer equal to 450and 700 psi. This ratio can be estimated as0.933+(1-0.933)*(600-450)/(700-450)=0.973, while the equivalent normalconcrete thickness of pavement should be estimated as 15*0.973=14.6inches.

[0035] The choice of the value of modulus of rupture of concrete ofsubbase and lower layer is determined by economical reasons.

DETAILED DESCRIPTION OF ADDITIONAL EMBODIMENT

[0036] Concrete of subbase and/or lower layer of composite concretepavement is produced with the use of coarse aggregate defined asenriched limestone quarry waste of grading intermediate between coarseand fine aggregates in Terminology of ASTM C125. Physical properties ofthis coarse aggregate should be in accordance with requirements of theASTM C33. This concrete is characterized by the specified compressivestrength f_(c)′ and modulus of rupture (MR) up to 5,000 and more than750 psi, respectively. Compressive strength of this concrete should behigher than that for concrete of the same consumption of cement withcrushed limestone of the Size number 89 as a coarse aggregate. Moreover,compressive strength of this concrete should be higher or at least closeto that for concrete of the same consumption of cement and twice as highconsumption of admixture with crushed granite of regular sizes as acoarse aggregate. Flexural strength of this concrete is higher than thatfor concrete of the same consumption of cement with crushed granite ofregular sizes as a coarse aggregates.

[0037] Limestone quarry waste is a by-product of manufacture of crushedlimestone of regular sizes mainly numbers 56, 57, 6 and 67 of the ratingdimensions 25-9.5 mm, 25-4.75 mm, 19-9.5 mm and 19-4.75 mm,respectively. As a raw material for enrichment it should be finer ⅜in.(9.5 mm) and coarser than 4.75 mm (Sieve No.4). Proportion betweenthe amounts of aggregate finer and coarser than 4.75 mm beforeenrichment is very important; the problem of utilization of aggregatefiner than 4.75 mm is more urgent than that for part of this by-productcoarser than 4.75 mm. Moreover, aggregate finer than 4.75 mm isconsiderably cheaper than part of this by-product coarser than 4.75 mm.According to the invention, the amount of aggregate finer than 4.75 mmat the quarry before enrichment should be at least the value of the sameorder as that for the least Size of coarse aggregate number 89 accordingto the ASTM C33 and not less than about ⅓ of the total weight ofaggregate.

[0038] Proportion between the amounts of aggregate finer and coarserthan 4.75 mm before enrichment should be determined taking into accountan inevitable breakdown of this aggregate due to dry enrichment byscreening and especially due to transportation of this aggregate toconcrete plant. The breakdown of aggregate is caused by weatherconditions (rain, frost, thawing) and handling of this aggregate(loading, discharge and other actions during transportation from quarryto aggregate bin of concrete plant). Due to the influence of scaleeffect this breakdown relates mainly to the portion of aggregate coarserthan 4.75 mm. As a result, amount of aggregate finer than 4.75 mm in theaggregate bin of concrete plant can be considerably higher than at thequarry. The amount of this fraction in the aggregate bin of concreteplant should be close to but not exceed ⅔ of the total weight ofaggregate. Transportation of the very vulnerable enriched limestonewaste of 10 percents water-absorption from quarry to the concrete plantunder adverse weather conditions results in the doubling the amount ofaggregate finer than 4.75 mm-from ⅓ to ⅔ of the total amount ofaggregate. Less water-absorption of aggregate and actual reduction ofthe quantity of adsorbed water means less breakdown of aggregate andmore similar proportions between amounts of aggregate finer and coarserthan 4.75 mm at the quarry and in the aggregate bin.

[0039] Enrichment of this by-product can be carried out by washing orscreening, or by combination of washing and screening separately forparts finer and coarser than 4.75 mm with consequent mixing of theseparts or without this separation. The aim of enrichment of limestonewaste is reduction of small size grains and to obtain the desirableproportion between the parts of aggregate. The choice of method ofenrichment depends on the results of sieve analysis of this aggregate,water-absorption of aggregate, and required grading of aggregate afterenrichment.

[0040] Due to the enrichment of limestone waste, the amount of smallSizes of grains at the quarry should be reduced. The amount of aggregatefiner than 2.36 mm (Sieve No. 8) should not exceed about 10%, the amountof aggregate finer than 1.18 mm (Sieve No. 16) should not exceed about7%, the amount of aggregate finer than 300μm (Sieve No. 50) should notexceed about 2%. The main part of aggregate finer than 4.75 mm should becoarser than 2.36 mm. The amount of aggregate coarser than 4.75 mm afterenrichment should be higher than ⅓ of the total weight of aggregate, andthis excess is determined by the volume of inevitable breakdown ofaggregate during the transportation to the aggregate bin of concreteplant. There are requirements of present invention for control ofgrading of enriched limestone waste as a coarse aggregate for concreteat the quarry after enrichment.

[0041] Transportation of enriched limestone waste from quarry to theaggregate bin of concrete plant causes the reduction of amount of largesize grains and a corresponding increase of the amount of small sizegrains since large size grains are more vulnerable. It can make gradingof this aggregate variable and even unpredictable. However, fewparameters of grading of enriched limestone waste after transportationfrom a quarry to the aggregate bin of a concrete plant should becontrolled in the framework of the present invention. The amount ofaggregate finer than 4.75 mm (Sieve No.4) should be less than for thelargest Size of fine aggregate number 9 according to ASTM C33. It shouldbe close to but not exceed ⅔ of the total weight of aggregate. The mainpart of aggregate finer than 4.75 mm should be coarser than 2.36 mm. Theamount of aggregate finer than 300 μm (Sieve No. 50) should not exceedabout 3.0%. Grading of enriched limestone waste as a whole aftertransportation can be considered borderline between coarse and fineaggregates in Terminology of ASTM C125, i. e. between grading of Sizesnumber 89 and 9 according to ASTM C33.

[0042] Experimental investigations of the washed by-product ofmanufacture of crushed limestone as a coarse aggregate for concrete werecarried out in Moscow Institute of Concrete and Reinforced Concrete(NIIZHB). These investigations were necessary due to the shortage andhigh cost of crushed granite as a coarse aggregate in the Moscow region;it was attempt to find more cheap coarse aggregate at least for concreteof middle strength. Enriched limestone waste product of Lavsk quarry ofLipetsk region (350 km South East of Moscow) was used for this purpose.This is the washed by-product of the manufacture of crushed limestone ofregular Russian Sizes 5-20 mm (the closest American Size is number 67,19-4.75 mm) and 20-40 mm defined as Russian fraction 3-10 mm.

[0043] Samples were taken from a large volume cone according to theRussian standard (very close to the similar ASTM standard) and weredelivered to Institute laboratory in bags retaining quarry grading afterenrichment of this aggregate. The crushing strength of limestone wastewas estimated by compressing in a 150 mm-diameter cylinder. Loss ofweight of tested samples made up 17%. According to the Russian buildingcode, this loss of weight corresponds to compressive strength of coarseaggregate equal to 600 kgf/cm{circumflex over ( )}2 (near 8500 psi).This is half as much as minimum strength of crushed granite Grades1200-1400 kgf/cm{circumflex over ( )}2.

[0044] Water-absorption of limestone waste is equal to 10%; specificgravity is equal to 2.46 g/cm{circumflex over ( )}3; bulk density isequal to 1390 kg/m{circumflex over ( )}3; the voids volume is estimatedas 43%.

[0045] Frost resistance of limestone waste was determined by the test ofsamples in the solution of sodium sulfate with subsequent drying. Theloss of mass after 10 cycles made up 10%. According to the Russianbuilding code, frost resistance of limestone waste is estimated as GradeF50. The content of dissoluble silica in limestone waste makes up 21milliliters per liter.

[0046] Samples of aggregate were dried to constant weight. Averagedresults of sieve analysis of enriched limestone waste as a coarseaggregate defined as fraction 3-10 mm according to the Russian buildingcode are presented in Table 3 in the form adopted in the US buildingpractice. TABLE 3 Dimensions of Square Openings (mm) Less 12.50 10.005.00 2.50 than 2.5 Sieve residue (%) 0.75 0.75 64.00 25.50 9.0 Amountfiner than each 99.25 98.5 34.50 9.00 — laboratory sieve (%)

[0047] As can be seen from Table 3, grading of this aggregate consideredas a quarry grading is close to that for Size number 89 as the leastSize of coarse aggregate according to ASTM C 33. Besides, a samples ofwashed finer limestone waste from a neighboring quarry defined as a 2-5mm Russian fraction of fine aggregate of grading close to that for thelargest Size of fine aggregate number 9 according to ASTM C 33 also wastested as a coarse aggregate of concrete. Physical properties ofaggregates fractions 3-10 and 2-5 are the same. It was made forestimation of change of concrete strength depending on the change ofgrading of small grains crushed limestone used as a coarse aggregate ofthis concrete. Moreover, comparison of concrete strength of samples withcoarse aggregate of the different grading allows estimation the changeof strengths of concrete caused by a possible breakdown of thisaggregate due to handling and transportation from quarry to aggregatebin of concrete plant. Results of sieve analysis of this aggregate(Russian fraction 2-5 mm) are presented in Table 4. TABLE 4 Dimensionsof Square Openings(mm) 5.0 2.5 1.25 0.63 0.315 0.16 under 0.16 Sieveresidue (%) 20.5 69.5 8.75 0.45 — — 0.8 Amount finer 79.50 10.00 1.250.8 0.8 0.8 than each laboratory sieve (%)

[0048] To estimate compressive strength of concrete with washedlimestone waste of fractions 3-10 and 2-5 mm as a coarse aggregatestandard cubes 10×10×10 cm were made with the use of Portland cementBrand 500-DO-N of the Oscol cement plant without admixture. According tothe Russian building practice of production of precast concrete cubeswere subjected to standard steam-curing according to following pattern;3+3+6+4, i.e. 3 hrs of conditioning, 3 hrs of the temperature rise to80° C., 6 hrs of isothermal warming, and 4 hrs of cooling. One-daycompressive strength of steam-cured concrete makes up 60-65% of 28-daystrength of this concrete. 28-day compressive strength of steam-curedconcrete makes up 90% of 28-day strength of concrete of naturalmaturing. Test results of compressive strength of concrete brought tothe standard European cube 15×15×15 cm and corresponding estimations ofcylindrical strength (psi) are presented in Table 5. Cylindricalstrength of concrete is estimated to be 1.2 times less than the cubicstrength of this concrete. Concrete mixes number 1, 3, 5 were made withenriched waste defined as a Russian fraction 3-10 mm (Table 3) as acoarse aggregate, mixes number 2, 4, 6 were made with an aggregatedefined as a Russian fraction 2-5 mm (Table 4) as a coarse aggregate.TABLE 5 Cubic compressive Composition of ready-mixed strength Mpa/Concrete (kg/m{circumflex over ( )}3) Cylindrical Water/ Density ofcompressive Coarse cement mix Slump strength psi Number Cement Sandaggregate ratio (kg/m{circumflex over ( )}3) (cm) 1 day 28 days 1 198751 1,068 1.05 2,225 6.5 5.8/690  10.0/1190  2 197 740 1,066 1.05 2,2107.0 4.8/570  8.0/950  3 347 596 1,091 0.61 2,245 8.0 19.4/2,31029.0/3,450 4 350 580 1,100 0.60 2,240 8.5 17.9/2,130 28.3/3,370 5 498478 1,075 0.43 2,265 7.5 37.1/4,420 42.0/5,000 6 500 483 1,060 0.422,255 9.0 31.1/3,700 38.4/4,570

[0049] As one can see from Table 5, the use of crushed limestone ofRussian fraction 3-10 mm with the grading close to that for Size No.89as a coarse aggregate for concrete allows to achieve compressivestrength of concrete in the range from 1,000 to 5,000 psi. Finer crushedlimestone of Russian fraction 2-5 mm of grading close to that for theSize number 9 is less efficient as a coarse aggregate. Compressivestrength of concrete with this coarse aggregate is less at least by 10%than that for concrete with coarse aggregate of grading close to thatfor the Size number 89.

[0050] All said above relates to concrete with coarse aggregate ofwashed limestone waste delivered to the Institute laboratory from thequarry without a change of its grading. It is necessary to estimate theactual breakdown of this aggregate due to transportation from quarry toplant and its impact on the concrete strength. The efficiency of the useof enriched limestone waste as a coarse aggregate in industrialconditions was checked at the Moscow plant of precast concrete No.10.Crushed limestone of the grading of Russian fraction 3-10 withwater-absorption equal to 10% as a very vulnerable coarse aggregate wasused for this aim. Ten double-side tipping wagons with 500 m{circumflexover ( )}3 of enriched limestone waste were delivered from the Lavskquarry to the concrete plant. Grading of this aggregate at the quarry ispresented in Table 3. Results of sieve analysis of this limestone wasteat the concrete plant are presented in the Table 6. TABLE 6 Dimensionsof Square Openings(mm) 10.0 5.0 2.5 1.25 0.63 0.315 0.16 Under 0.16Sieve residue (%) 2.4 30.6 58.7 3.0 0.9 1.66 2.2 0.54 Amount finer thaneach 2.4 67.0 8.3 5.3 4.4 2.74 0.54 — laboratory sieve (%)

[0051] As can be seen from the Table 6, grading of enriched limestonewaste at the concrete plant considerably differs from the grading ofthis aggregate at the quarry after enrichment. It changes due toloading, autumn rains, and moving by bulldozers to aggregate bin afterdischarge from wagons on concrete pavement of the concrete plant store.The amount of aggregate finer than 5 mm constituted near ⅓ of the totalweight of aggregate before transportation to the concrete plant, whilethe amount of this aggregate at the concrete plant is close to the ⅔ ofthe total weight of aggregate. The main part of aggregate is finer than5 mm and coarser than 2.5 mm. Grading of enriched limestone waste aftertransportation to the concrete plant can be considered close tointermediate between coarse and fine aggregates in Terminology of ASTMC125, i. e. between grading of Sizes number 89 and 9 according to ASTMC33.

[0052] The tests of concrete with limestone waste of this grading werecarried out, the consumption of cement being the same as for prestressedpiles. It was made to estimate maximum compressive strength of concretewith crushed limestone as a coarse aggregate of this grading. Concretefor piles is produced only with granite crushed stone as a coarseaggregate, and consumption of portland cement Brand 500-DO-N of theVolsk cement plant for this concrete is equal to 460 kg per cubic meterof concrete. The peculiarity of concrete for prestressed piles is therequired one-day cubic compressive strength, which should be not lessthan 30 Mpa. This cubic strength corresponds to a cylindrical strengthequal to 3570 psi. According to the Russian building practice ofproducing of precast concrete, cubes were subjected to the standardsteam-curing according to next pattern; 3+3+6+4, i.e. 3 hrs ofconditioning, 3 hrs of the temperature rise to 80° C., 6 hrs ofisothermal warming, and 4 hrs of cooling. Test results of concrete arepresented at the Table 7. TABLE 7 Cubic compressive strength MpaComposition of ready- Cylindrical mixed concrete (kg/m{circumflex over( )}3) compressive Water/ strength psi Coarse cement Admixture Slump 1day 28 days Number Cement Sand aggregate ratio (%) (cm) f_(cu) f_(cuavg)f_(cu) f_(cuavg) 1 500 483 1060 0.324 — 6 20.9 22.60 29.9 30.60 24.32,960 33.3 3,640 2 500 483 1060 0.308 0.5 7 21.8 21.10 30.4 29.45 20.52,510 28.5 3,505 3 500 483 1060 0.420 — 8 20.9 20.65 39.9 39.45 20.42,460 39.4 4,700 4 500 512 1110 0.370 — 6 23.8 24.50 46.5 46.05 25.22,920 45.6 5,480 5 500 512 1110 0.280 0.3 6 41.8 42.00 46.1 47.75 42.25,000 49.4 5,685 6 450 560 1110 0.280 0.3 6 35.6 34.80 40.9 40.40 33.74140 39.9 4,810 7 400 610 1110 0.280 0.3 4 32.3 34.20 43.2 43.45 36.14070 43.7 5,170

[0053] Three first series of test can be considered as attempts offitting to very unusual coarse aggregate; crushed limestone was not usedas a coarse aggregate on the plant. Four other series of test of thisconcrete should be considered as quite successful. Enriched limestonewaste as a coarse aggregate after considerable breakdown caused by thehandling and transportation to the concrete plant in the adverse weatherconditions allows to obtain concrete of specified compressive strengthup to 5,000 psi and even more.

[0054] The efficiency of enriched limestone waste of the certain gradingas a coarse aggregate can be estimated by the compressive strength ofconcrete with this coarse aggregate. As can be seen from the Tables 5and 7, enriched limestone waste of grading intermediate between thecoarse and fine aggregate in Terminology ASTM C125 is more efficient asa coarse aggregate than crushed limestone of grading close to that forthe Size No.89 and grading close to that for the Size No.9 according tothe ASTM C33. Compressive strength of concrete with crushed limestone ofthis grading as a coarse aggregate is higher at least by the 10% thanthat for concrete of the same consumption of cement with crushedlimestone of grading close to that for the Size No.89 as a coarseaggregate. Compressive strength of this concrete is considerably higherthan that for concrete of the same consumption of cement with crushedlimestone of grading close to that for the Size No.9 as a coarseaggregate. Moreover, consumption of cement for concrete with crushedlimestone as a coarse aggregate of grading intermediate between thecoarse and fine aggregate in Terminology ASTM C125 is less at least bythe 10% than that for concrete of the same compressive strength withcrushed granite of regular sizes as a coarse aggregate. One-day concretestrength exceeding the required for prestressed piles was achieved withreduction of the consumption of cement by more than ten-percent less andthe half as many consumption of admixture as compared with that forconcrete with crushed granite as a coarse aggregate (Tables 5 and 7).

[0055] Thus, crushed limestone of the amount of aggregate finer than4.75 mm close to but not exceeding ⅔ of the total weight of aggregate,of the amount of aggregate finer than 4.75 mm but coarser than 2.36 mmin the range 55-60% of the total weight of aggregate, of the amount ofaggregate finer than 0.3 mm not exceeding about 3% of the total weightof aggregate can be considered as a coarse aggregate of optimal gradingin terms of compressive strength of concrete. This grading can beconsidered as intermediate between the coarse and fine aggregate in theTerminology ASTM C125. Concrete with crushed limestone of this gradingas a coarse aggregate requires less consumption of cement and admixturethan concrete of the same compressive strength with crushed granite andany hard rock aggregate of regular sizes as a coarse aggregates.Concrete with crushed limestone of this grading as a coarse aggregaterequires less consumption of cement than concrete of the samecompressive strength with crushed limestone of grading corresponding tothat for Sizes number 89 and 9 according to the ASTM C33 as a coarseaggregate.

[0056] Variation of grading of enriched limestone waste is inevitable;it is in the nature of this material. Requirements for grading ofenriched limestone waste as a coarse aggregate at the quarry afterenrichment and in the aggregate bin of concrete plant should limitinfluence of variation of grading of this aggregate on the strength ofconcrete. However, adverse conditions of transportation of thisaggregate to the concrete plant can cause its excessive breakdown. Itdoes not mean that enriched limestone waste of this grading can not beused as a coarse aggregate for concrete. However excessive breakdown ofthis coarse aggregate influences the strength of concrete. If the amountof aggregate finer than 4.75 mm exceeds ⅔ of the total weight ofaggregate in the aggregate bin, it means reduction of concrete strength.Additional consumption of cement requires for compensation ofdegradation of this aggregate.

[0057] Tests of concrete with the different grading of crushed limestoneas a coarse aggregate allow to estimate the acceptable limits ofvariation of grading of enriched limestone waste as a coarse aggregatein aggregate bin of concrete plant. As can be seen from the Tables 5 and7, compressive strength of concrete with crushed limestone of gradingclose to that for the Size No.9 is less at least by 10% than that forconcrete with crushed limestone of grading close to that for the SizeNo.89. Compressive strength of this concrete is considerably less thatfor concrete with crushed limestone of grading intermediate between thecoarse and fine aggregate in the Terminology ASTM C125. The use ofenriched limestone waste of grading finer than that for the Size number9 as a coarse aggregate should be considered as undesirable; additionalbreakdown of aggregate requires non-proportional increase of consumptionof cement.

[0058] Flexural strength of concrete is important quality of concrete.As applied to the thickness design of concrete pavement, flexuralstrength is the main quality of concrete. Concrete with crushedlimestone as a coarse aggregate of grading intermediate between thecoarse and fine aggregates in the Terminology ASTM C125 can beconsidered as optimal in terms of flexural strength at least as comparedwith concrete with hard rock coarse aggregates of regular sizes.Compressive strength of concrete with this coarse aggregate is higherthan that for concrete of the same consumption of cement with crushedgranite of regular sizes as a coarse aggregate, and the increase ofcompressive strength of concrete means the increase of flexural strengthof this concrete.

[0059] As the strength of any structural material flexural strength ofconcrete should be characterized by the specified value, design flexuralstrength being estimated as a part of specified flexural strength.American building code ACI 318 and documents of Portland CementAssociation do not contain the definition of specified concrete flexuralstrength. Current of thickness design procedure of concrete pavementsallows considering the modulus of rupture (MR) as a specified concreteflexural strength. According to said Portland Cement AssociationEngineering Bulletin (Thickness Design for Concrete Highway and StreetPavements, Portland Cement Association, EB109P), the modulus of rupture(MR) of concrete should be estimated as the average 28-day flexuralstrength. The value of flexural strength multiplied by 50 psi, which isless than the experimental estimation of the mean value of this strengthbut is nearest to it, should be chosen as the modulus of rupture (MR) ofthis concrete.

[0060] It is well known that flexural strength is not inherent qualityof concrete as well as compressive strength. Compressive strength ofconcrete is the best studied quality of concrete, and it is veryimportant to provide means for estimation of statistical characteristicsof flexural strength of concrete by means of those for compressivestrength of this concrete. Statistical characteristics of flexuralstrength of normal concrete in connection with those for compressivestrength of this concrete were obtained by processing the data of theresults of American tests of cylindrical compressive strength andflexural strength of concrete, and American and British tests of thecompressive strength of modified cubes and the flexural strength ofconcrete (Sapozhnikov N. Safety of Precast Reinforced Concrete andPrestressed Structural Members by the Second Limit State (ServiceabilityLimit State). State Committee of Construction of the USSR Institute ofInformation, Moscow, 1991, Table 6, FIG. 8).

[0061] Statistical connections between compressive and flexural strengthof concrete were estimated by the values of coefficient of correlationbetween these two types of concrete strength. Coefficients ofcorrelation between the compressive and flexural concrete strength areequal to 0.831 and 0.865 for two big samplings of test results of 3650standard cylinders and beams and 1107 modified cubes and standard beams,respectively. Connections between compressive and flexural concretestrength, which correspond to these values of coefficient ofcorrelation, can be considered statistically significant. It allows thechoice of modulus of rupture of concrete (MR) of concrete for thicknessdesign of pavement depending on the specified compressive strength ofthis concrete.

[0062] Using the test result of 3,650 of standard cylinders and beams,the mean value of flexural strength of concrete f_(r) can be estimateddepending on the mean value of cylinder compressive strength f_(c) asequal to 9.424

f_(c). This estimation of the mean value of flexural strength ofconcrete corresponds to the theoretical line of linear regressionbetween compressive and flexural strength of concrete. It can beconsidered as legitimate at least in the range of the change ofcompressive strength from 2,500 to the 4,750 psi; as can be seen fromthe FIG. 8, theoretical and empirical lines of regression in this rangeof change of compressive strength coincide completely. Since thedeviation of empirical line of regression from theoretical one is smallup to compressive strength of concrete equal to 6,000 psi, estimation ofthe mean value of flexural strength equal to 9.42

f_(c) can be considered as legitimate in the range of change compressivestrength from 2,500 to 6,000 psi.

[0063] Since the main estimation of compressive strength of concrete inAmerican building practice is cylinder strength, the modified cubestrength was assessed as cylinder by dividing by 1.2; the cubic strengthof concrete is higher than that of cylindrical by 20% on average. Usingthe test results of 1107 of modified cubes and standard beams, the meanvalue of flexural strength of concrete f_(r) can be estimated dependingon the mean value of modified cubes compressive strength of thisconcrete f_(cu.mod) is equal to 9.534

f_(cu.mod)/1.2. Estimations of the mean value of the flexural strengthof concrete obtained depending on the mean values of the compressivecylindrical and modified cubes strength of this concrete brought tocylindrical strength are very close and can be considered adequate.

[0064] According to said American building code ACI 318, the mean valueof compressive strength of concrete f_(c) considered as the requiredaverage strength f_(cr) in terms of the ACI 318 must exceed thespecified compressive strength f_(c)′ by at least 1.34S(f_(c)), whereS(f_(c)) is the standard deviation of this strength. The values of thecoefficient of variation for compressive and flexural strength ofconcrete are assumed usually as equal to 15% (Thickness Design forConcrete Highway and Street Pavements, Portland Cement Association,EB109P, p. 34). Basing on value of coefficient of variation equal to15%, this excess can be estimated as 25% of value of specifiedcompressive strength f_(c)′. Thus, the mean value of compressivestrength of concrete f_(c) can be considered as corresponding to certainvalue of specified compressive strength f_(c)′. Due to close statisticalconnections between the compressive and flexural strength of concrete,mean value of flexural strength of this concrete f_(r) estimated as9.424

f_(c) can also be considered as corresponding to this value of specifiedcompressive strength.

[0065] The value of flexural strength multiplied by 50 psi, which isless than the estimation of the mean value of this strength but isnearest to it, should be chosen as the modulus of rupture (MR) of thisconcrete. Values of specified compressive strength f_(c)′ equal to3,000, 3,500, 4,000, 4,500 and 5,000 psi corresponds to the values ofmodulus of rupture (MR) equal to 550, 600, 650, 700, and 750 psi,respectively, coefficient of variation of compressive strength ofconcrete being assumed as 15%. These estimations of modulus of ruptureof concrete are stable as to the change of coefficient of variation ofcompressive strength of concrete.

[0066] The large sampling of test results of 3650 standard cylinders andbeams includes the 81 series of concrete samples of the same mix design.The coefficients of variation of compressive and flexural strength wereestimated for all these series. The mean value of coefficient ofvariation of compressive strength of 81 series of test results ofstandard cylinder constitutes 10.95%. According to the requirements ofACI 318, required average strength should exceed specified compressivestrength at least by 17%. Values of specified compressive strengthf_(c)′ equal to 3,000, 3,500, 4,000, 4,500 and 5,000 psi corresponds tothe values of the required average compressive strength equal to 3,510,4,095, 4,680, 5,625, and 5,850 psi, respectively. The mean values offlexural strength corresponding to these values of the required averagecompressive strength estimated by the plot of change flexural strengthof concrete depending on the change of the compressive strength (FIG. 8)are very close to 550, 600, 650, 700, and 750 psi, respectively.

[0067] As can be seen on the FIG. 8, empirical and theoretical lines ofregression do not coincide in the range of change of compressivestrength of concrete from 1,000 to 2,000 psi. The values of flexuralstrength of concrete in this range of the change of compressive strengthare estimated as corresponding to the empirical line of regression. Thevalues of compressive strength equal to 1,000, 1,500, and 2,000 psicorrespond to the values of flexural strength equal to 250, 350, and 450psi, respectively. The volume of test results in this range of thechange of compressive strength is not good enough for estimation ofvalues of modulus of rupture depending on the specified compressivestrength of concrete. Because of this, the values of flexural strengthequal to 300, 400, and 450 psi only approximately can be considered asthe estimations of modulus of rupture corresponding to the values ofspecified compressive strength equal to 1,000, 1,500, and 2,000 psi,respectively.

[0068] The foregoing estimations of the values of the modulus of ruptureof concrete depending on the values of specified compressive strengthf_(c)′ of this concrete are based on the test results of concrete withall types of coarse aggregate of regular sizes. Considerable part ofthese aggregates relates to the hard rock (gravel, crushed gravel, andcrushed granite). It is well known that flexural strength of concretewith this coarse aggregate is in the range from 10 to2 percents ofcompressive strength of concrete, and it increases up to the 15 percentsof compressive strength for concrete with crushed limestone of regularsizes as a coarse aggregate.

[0069] It can be waited the higher flexural strength of concrete withsmall grains crushed limestone as a coarse aggregate than that forconcrete of the same consumption of cement with crushed limestone ofregular sizes as a coarse aggregate. It is possible due to more completepenetration of mortar into small grains crushed limestone and moreuniform structure of concrete with this coarse aggregate than that forconcrete of crushed limestone of regular sizes as a coarse aggregate.The first flexural tests of concrete with crushed limestone as a coarseaggregate of grading intermediate between that for coarse and fineaggregate in the Terminology ASTM C125 confirm this tendency. In thesetests the values of flexural strength of concrete equal to 418, 657 and771 psi correspond to the values of compressive strength equal to 1,476,2,821, and 4,166 psi, respectively. Flexural strength of concrete inthese tests is in the range from 28.35 to 18.5 percents of compressivestrength, diminishing with the increase of compressive strength. It doesnot mean the possibility of such estimations of modulus of rupture ofconcrete depending on the compressive strength of this concrete. Thereare only test results of the 3 series of two standard cubes brought tocylinder strength and two standard beams. However it means the tendencywhich should be checked during the mass production of concrete withcrushed limestone of this grading for road construction.

[0070] An estimation of coefficient of variation of normal concretestrength equal to 15% is usually assumed and is incorporated into thedesign charts and tables of ACI and Portland Cement Associationdocuments both for compressive and flexural strength. Concrete withenriched limestone waste as a coarse aggregate is more homogenous thanconcrete with crushed granite and crushed limestone of regular sizes asa coarse aggregate. The degree of uniformity of this concrete can beconsidered as intermediate between that for normal concrete with coarseaggregate of regular sizes and mortar. It means that the coefficient ofvariation of strength of concrete with the enriched limestone waste ascoarse aggregate should be less than for concrete with coarse aggregateof regular sizes. Reduction of coefficient of variation of compressivestrength of concrete means the possibility to reduce compressive averagestrength required according to said American building code ACI 318 withcorresponding reduction of consumption of cement for this concrete. Themain peculiarity of concrete with limestone quarry waste as a coarseaggregate is the possibility of utilization of great deposits of crushedlimestone finer than 9.5 mm, and especially the part of this aggregatefiner than 4.75 mm. The minimum of aggregate finer than 4.75 mm beforeenrichment constitutes near ⅓ of the total weight of aggregate, and itcorresponds to very vulnerable aggregate. The use of less vulnerableaggregate means the possibility of reduction of the amount of aggregatecoarser than 4.75 mm and corresponding increase of the amount ofaggregate finer than 4.75 mm before enrichment. Utilization of greatdeposits of limestone waste enables to reduce quarrying of high-qualityaggregate with corresponding conservation of environment.

[0071] Concrete with crushed limestone of grading intermediate betweenthe coarse and fine aggregates in the Terminology ASTM C125 was checkedin industrial conditions. Crushed limestone of this grading was used asa coarse aggregate for concrete of precast reinforced concrete temporaryroad slabs 1.75×3.0×0.16 m dimensions. More than 500 these slabs wereproduced on September-October 2002 at this plant. These slabs are usedfor access roads to buildings under construction. They are placedusually into mud without any subbase and work separately. Conditions ofservice of these slabs under extensive truck traffic are more thanadverse. However there are no financial claims to plant connected withthe strength of those slabs.

[0072] The use of concrete with this coarse aggregate allows veryprofitable utilization of great deposits of crushed limestone finer than9.5 mm usually estimated as limestone quarry waste and especiallyaggregate finer than 4.75 mm. In so doing the volume of utilizedaggregate finer than 4.75 mm should constitutes at least ⅓ of the volumeof utilized aggregate finer than 9.5 mm.

OPERATION OF ADDITIONAL EMBODIMENT

[0073] The main aim of operation is to obtain concrete with enrichedlimestone waste as a coarse aggregate of grading optimal in terms ofcompressive and flexural strength of concrete. It means that in theaggregate bin of concrete plant the amount of aggregate finer than 4.75mm should be close to but not exceed ⅔ of the total weight of aggregate,the amount of aggregate finer than 4.75 mm but coarser than 2.36 mmshould be about 55-60% of the total weight of aggregate, the amount ofaggregate finer than 0.3 mm should not exceed about 3% of the totalweight of aggregate. Cost of aggregate finer than 9.5 mm and coarserthan 4.75 mm depends on the proportion between amounts of aggregatefiner and coarser than 4.75 mm before enrichment; cost of aggregatefiner than 4.75 mm is considerably less than that for aggregate coarserthan 4.75 mm.

[0074] Amount of aggregate finer than 4.75 mm before enrichment shouldbe not less than ⅓ of the total weight of aggregate. It is determineddepending on the breakdown of this aggregate due to handling andtransportation to aggregate bin of concrete plant. Since more coarseparts of aggregate are more vulnerable due to scale effect, breakdown ofaggregate relates mainly to its part coarser than 4.75 mm. Breakdown ofaggregate depends on the its water-absorption, weather conditions,conditions of handling and transportation, and should be estimatedexperimentally. The breakdown of aggregate of ten-percentwater-absorption under adverse weather conditions, adverse conditions ofhandling and transportation to aggregate bin of concrete plant resultsin the doubling increase of aggregate finer than 4.75 mm. Breakdown ofaggregate of less water-absorption should be less, and proportionsbetween amounts of aggregate of finer and coarser than 4.75 mm beforeenrichment and in aggregate bin of concrete plant should be closer.Moreover, breakdown of aggregate coarser than 4.75 mm caused byscreening as a dry enrichment of aggregate should be taking into accountalso.

[0075] Excessive breakdown of enriched limestone waste as a coarseaggregate causes reduction of concrete strength, which should becompensated by additional consumption of cement. Grading of crushedlimestone finer than corresponding to the Size number 9 is consider asunacceptable for its utilization as a coarse aggregate since it requiresincrease of consumption of cement non-proportional to degradation ofaggregate.

[0076] Enrichment can be carried out by washing or screening, or bycombination of washing and screening. The aim of enrichment is reductionof is reduction of small size grains and to obtain the desirableproportion between the parts of aggregate. The choice of method ofenrichment depends on the results of sieve analysis of this aggregateand the domestic conditions.

[0077] Mix design of concrete with crushed limestone of this gradingshould be carried out with the consumption of cement less by about 10%and twice less consumption of admixture than that required for concreteof the same specified compressive strength with crushed limestone ofregular sizes as a coarse aggregate. Batch plant corrections must bemade for moisture in aggregates.

CONCLUSION

[0078] Composite concrete pavement includes the surface course of normalconcrete and subbase and/or lower layer with compressive and flexuralstrength which can be no less than that for normal concrete of surfacecourse. Coarse aggregate of subbase and/or lower layer concrete definedas enriched limestone waste is a washed by-product of manufacture ofcrushed limestone of ordinary Sizes number 56, 57, 6, and 67 with rateddimensions 25-9.5 mm, 25-4.75 mm, 19-9.5 mm, and 19-4.75 mm,respectively. Enrichment of this aggregate should be carried out bywashing or screening, or by combination of washing and screening. Methodof enrichment depends on the grading of aggregate and should be selectedby economical reasons.

[0079] Limestone quarry waste as a raw material for enrichment should becoarser than 9.5 mm and finer than 4.75 mm. The amount of aggregatefiner than 4.75 mm (Sieve No.4) before enrichment should be at least thevalue of the same order as for least Size of coarse aggregate number 89according to ASTM C 33. It should be not less than ⅓ of total weight ofaggregate. After enrichment the main part of aggregate finer than 4.75mm should be coarser than 2.36 mm. The amount of aggregate finer than2.36 mm (Sieve No. 8) should not exceed about 10%; the amount ofaggregate finer than 1.18 mm (Sieve No. 16) should not exceed about 7%;the amount of aggregate finer than 300μm (Sieve No. 50) should notexceed about 2%.

[0080] Grading of this aggregate at the quarry after enrichment and inthe aggregate bin of concrete plant differs due to inevitable breakdownof aggregate caused by handling and transportation from quarry toconcrete plant. Due to scale effect large grains are more vulnerable,and breakdown of aggregate relates mainly to part of aggregate coarserthan 4.75 mm. As a result, amount of aggregate finer than 4.75 mm aftertransportation to aggregate bin of concrete plant should be increased.The breakdown of aggregate should be estimated experimentally and takinginto consideration when determining of proportion between parts ofaggregate finer and coarser than 4.75 mm before enrichment of thisaggregate.

[0081] The amount of aggregate finer than 4.75 mm in aggregate binshould be close to but not exceed ⅔ of the total weight of aggregate.The main part of aggregate finer than 4.75 mm should be coarser than2.36 mm. The amount of aggregate finer than 300μm (Sieve No. 50) shouldnot exceed about 2%. Grading of enriched limestone waste in aggregatebin should be finer than the least Size of coarse aggregate number 89and coarser than for largest Size of fine aggregate number 9 accordingto ASTM C 33. This grading can be considered as intermediate between thecoarse and fine aggregates in Terminology of ASTM C125.

[0082] This grading of crushed limestone as a coarse aggregate can beconsidered as optimal in terms of concrete strength. Compressivestrength of concrete with crushed limestone of grading corresponding tothat for Sizes 89 and 9 as a coarse aggregate is less at least by 10%than compressive strength of concrete of the same consumption of cementwith crushed limestone of this grading as a coarse aggregate. Moreover,compressive strength of concrete with crushed granite of regular sizesis less than compressive strength of concrete of the same consumption ofcement and twice less consumption of admixture with crushed limestone ofthis grading as a coarse aggregate.

[0083] Variation of grading of enriched limestone waste is inevitableand excessive degradation of this aggregate should be considered as apossible. Excessive breakdown of aggregate does not mean impossibilityof its use as a coarse aggregate for concrete. However it requiresadditional consumption of cement; grading of aggregate finer thancorresponding to the Size number 9 is consider as unacceptable.

[0084] Enriched limestone waste is one of the cheapest aggregates.However, use of this aggregate allows obtaining concrete of specifiedcompressive strength f_(c)′ and modulus of rupture (MR) up to 5,000 and700 psi, respectively. Using of this concrete for subbase and/or lowerlayer allows considerable reduction of thickness of normal concretesurface course; its thickness is determined by the requirements forabrasion resistance of a normal concrete surface. The use of concrete ofthe different cost but of the same compressive and flexural strength fordifferent parts of composite pavement allows to obtain compositeconcrete pavement of the equivalent normal concrete thickness equal tothe physical one.

[0085] The use of very cheap and very efficient concrete with enrichedlimestone waste as a coarse aggregate for composite concrete pavementallows reduction of initial cost of construction of this pavement andmakes this pavement more competitive as compared with asphalt pavement.Moreover, the use of concrete with this coarse aggregate allows veryprofitable utilization of great deposits of crushed limestone finer than9.5 mm usually estimated as limestone quarry waste and especiallyaggregate finer than 4.75 mm. In so doing the volume of utilizedaggregate finer than 4.75 mm should constitutes at least ⅓ of the volumeof utilized aggregate finer than 9.5 mm. Utilization of limestone wasteenables to reduce quarrying of high-quality aggregate with correspondingconservation of environment.

1. Composite concrete pavement with the surface course of normalconcrete and subbase and/or lower layer of compressive and flexuralstrength of concrete which can be not less than that of surface coursenormal concrete with the same consumption of cement, specifiedcompressive strength f_(c)′ and modulus of rupture (MR) of subbase andlower layer concrete amount up to 5,000 and more than 750 psi,respectively, coarse aggregate of subbase and lower layer concretedefined as enriched limestone waste is processed by-product ofmanufacture of crushed limestone of regular Sizes number 56, 57, 6 and67 with rated dimensions 25-9.5 mm, 25-4.75 mm, 19-9.5 mm and 19-4.75mm, respectively, physical properties of this coarse aggregate should bein accordance with requirements of ASTM C 33, thickness of surfacecourse of composite pavement is determined by requirements for abrasionresistance, lower layer of pavement is monolithic with surface course,if flexural concrete strength of the surface course, subbase, and lowerlayer are the same, the equivalent normal concrete thickness ofcomposite pavement should be close to its physical one.
 2. Concrete ofsubbase and/or lover layer of composite concrete pavement of claim 1 ofspecified compressive strength f_(c)′ and modulus of rupture (MR) up to5,000 and more than 750 psi, respectively, with the coarse aggregatedefined as enriched limestone waste which is processed by-product ofmanufacture of crushed limestone mainly of regular Sizes numbers 56, 57,6, and 67 with the rated dimensions 25-9.5 mm, 25-4.75 mm, 19-9.5 mm,and 19-4.75 mm, respectively, this by-product as a raw material forenrichment should be finer than ⅜ in.(9.5 mm) and coarser than 4.75 mm(Sieve No.4), enrichment of this by-product can be carried out bywashing or screening, or by a combination of washing and screeningseparately for parts finer and coarser than 4.75 mm with consequentmixing of these parts or without this separation depending on theresults of sieve analysis of this aggregate, amount of aggregate finerthan 4.75 mm at quarry before enrichment should be at least the value ofthe same order as that of the least Size of coarse aggregate number 89according to ASTM C 33 and not less than about ⅓ of the total weight ofaggregate, the proportions between the amounts of aggregate finer andcoarser than 4.75 mm before enrichment should be determined taking intoaccount an inevitable breakdown of aggregate due to handling andtransportation from quarry to the aggregate bin of a concrete plant,after enrichment of limestone waste the amount of aggregate finer than2.36 mm (Sieve No.8) should not exceed about 10% of the total weight ofaggregate, the amount of aggregate finer than 1.18 mm (Sieve No. 16)should not exceed about 7% of the total weight of aggregate, the amountof aggregate finer than 300 μm Sieve No. 50) should not exceed about 2%of the total weight of aggregate, after transportation of aggregate toconcrete plant the amount of aggregate finer than 4.75 mm should be lessthan that of the largest Size of fine aggregate number 9 according toASTM C33 and close to but not exceeding ⅔ of the total weight ofaggregate, the amount of aggregate finer than 300 μm (Sieve No.50)should not exceed about 3.0% of the total weight of aggregate, gradingof enriched limestone waste after transportation to the aggregate bin ofconcrete plant should be finer than that for the least Size of coarseaggregate Number 89 and coarser than that for the largest Size of fineaggregate Number 9 according to ASTM C33 and can be considered asintermediate between the coarse and fine aggregates in Terminology ofASTM C125, physical properties of this coarse aggregate should be inaccordance with requirements of ASTM C33, compressive strength ofconcrete should be higher than that for concrete of the same consumptionof cement with crushed limestone of the Size Number 89 as a coarseaggregate and higher or at least close to that for concrete of the sameconsumption of cement and twice as high consumption of admixture withcrushed granite of regular sizes as a coarse aggregate while theflexural strength of this concrete is higher than that for concrete ofthe same consumption of cement with crushed granite as a coarseaggregate, the values of the modulus of rupture (MR) of concrete equalto 550, 600, 650, 700, and 750 psi correspond to the values of thespecified compressive strength f_(c)′ of this concrete equal to 3,000,3,500, 4,000, 4,500, and 5,000 psi, respectively.